/*
 *                               POK header
 *
 * The following file is a part of the POK project. Any modification should
 * be made according to the POK licence. You CANNOT use this file or a part
 * of a file for your own project.
 *
 * For more information on the POK licence, please see our LICENCE FILE
 *
 * Please follow the coding guidelines described in doc/CODING_GUIDELINES
 *
 *                                      Copyright (c) 2007-2021 POK team
 */

/* e_logf.c -- float version of e_log.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#ifdef POK_NEEDS_LIBMATH

#include "math_private.h"

static const float ln2 = 0.6931471805599452862268,
                   two25 = 3.355443200e+07, /* 0x4c000000 */
    Lg1 = 6.6666668653e-01,                 /* 3F2AAAAB */
    Lg2 = 4.0000000596e-01,                 /* 3ECCCCCD */
    Lg3 = 2.8571429849e-01,                 /* 3E924925 */
    Lg4 = 2.2222198546e-01,                 /* 3E638E29 */
    Lg5 = 1.8183572590e-01,                 /* 3E3A3325 */
    Lg6 = 1.5313838422e-01,                 /* 3E1CD04F */
    Lg7 = 1.4798198640e-01;                 /* 3E178897 */

static const float zero = 0.0;

float __ieee754_log2f(float x) {
  float hfsq, f, s, z, R, w, t1, t2, dk;
  int32_t k, ix, i, j;

  GET_FLOAT_WORD(ix, x);

  k = 0;
  if (ix < 0x00800000) { /* x < 2**-126  */
    if ((ix & 0x7fffffff) == 0)
      return -two25 / zero; /* log(+-0)=-inf */
    if (ix < 0)
      return (x - x) / zero; /* log(-#) = NaN */
    k -= 25;
    x *= two25; /* subnormal number, scale up x */
    GET_FLOAT_WORD(ix, x);
  }
  if (ix >= 0x7f800000)
    return x + x;
  k += (ix >> 23) - 127;
  ix &= 0x007fffff;
  i = (ix + (0x95f64 << 3)) & 0x800000;
  SET_FLOAT_WORD(x, ix | (i ^ 0x3f800000)); /* normalize x or x/2 */
  k += (i >> 23);
  dk = (float)k;
  f = x - (float)1.0;
  if ((0x007fffff & (15 + ix)) < 16) { /* |f| < 2**-20 */
    if (f == zero)
      return (dk);
    R = f * f * ((float)0.5 - (float)0.33333333333333333 * f);
    return (dk - (R - f) / ln2);
  }
  s = f / ((float)2.0 + f);
  z = s * s;
  i = ix - (0x6147a << 3);
  w = z * z;
  j = (0x6b851 << 3) - ix;
  t1 = w * (Lg2 + w * (Lg4 + w * Lg6));
  t2 = z * (Lg1 + w * (Lg3 + w * (Lg5 + w * Lg7)));
  i |= j;
  R = t2 + t1;
  if (i > 0) {
    hfsq = (float)0.5 * f * f;
    return (dk - (hfsq - s * (hfsq + R) - f) / ln2);
  } else
    return (dk - ((s * (f - R)) - f) / ln2);
}
#endif
